Method of treating hydrophilic colloids to avoid selling during washing



Patented June 28, 1949 METHOD OF TREATING HYDROPHILIC COL- LOIDS TOAVOID SWELLING DURING WASHING William D. Ramage, Berkeley, Calif.,assignor to United States of America as represented by the Secretary ofAgriculture No Drawing. Application April 22, 19's, Serial No. 743,211

(Granted under theact of March 3, 1883, as amended April 30, 1928; 370O. G. 757) 12 Claims.

This application is made under the act of March 3, 1883, as amended bythe act of April 30, 1928, and the invention herein described, ifpatented, may be manufactured and used by or for the Government of theUnited States of America for governmental purposes without the paymentto me of any royalty thereon.

This application is a continuation-in-part of my copending patentapplication Serial No. 703,971, filed Oct. 18, 1946, now abandoned.

This invention relates to a method of treating hydrophilic colloids toavoid swelling during washing thereof and without impairing thesubsequent swelling power or capacity of the material. It is directedparticularly to a method for washing hydrophilic colloidal substanceswhich are contaminated by the presence of water-soluble electrolytes orother water-soluble impurities and which colloidal substances swell inwater in the absence of electrolytes.

' Thus this invention is directed to the purification, by washing, of a'particular class of hydrophilic colloidal substances, i. e., thosecolloidal substances the swelling capacity in water of which increasesas the concentration of electrolytes is decreased. Some hydrophiliccolloidal substances, such as gelatin and high-methoxyl pectins, willswell, even in the presence of electrolytes. Thus colloidal substancesof this type can be applied to their ultimate uses, even though they maybe contaminated with water-soluble electrolytes. Consequently, althoughmy invention may be applied to colloidal substances of this type, thereis no particular advantage in so doing. On the other hand, inthe case ofhydrophilic colloids, the swelling capacity of which increases as theconcentration of electrolytes is decreased, the removal of theelectrolyte impurity is very important. presence of such impurityprevents application of the colloidal substance to uses wherein themaximum swelling is desired. Thus my invention is of particularimportance with respect to colloidal substances of the latter type. Myinvention is also applicable to the removal of sugars and otherwater-soluble non-electrolyte impurities from colloidal substances ofthe latter type.

Since the gelling power or hydration-capacity of many hydrophiliccolloidal substances is greatly diminished by even low concentrations ofelectrolytes (Reitz et 211., Industrial and Engineering Chemistry, vol.36, pp. 1149-1151 (1944)) it is important that soluble electrolytes bealmost completely removed during manufacture of the gelling substance.However, when this purification is carried out by washing with water,the concentra- Thetion of electrolyte is progressively reduced and thisin turn causes more and more swelling of the colloidal substance.Consequently, each washing operation becomes more time consuming andrequires very large vessels in the final stages for very small amountsof the product. For example, in washing sodium gluten sulphate (whichmay be prepared from wheat gluten by the processes described in theReitz Patent 2,344,267 and in Reitz application Serial No. 611,216,filed Aug. 17, 1945) by ordinary water washing, the final washes aredone on a gel containing less than one-half of one percent of solids.Thus the required ratio of water to solids is considerably more than 200to 1 in order to effect any appreciable removal of electrolytes in thefinal washings. Separation of the wash water from the gel is alsoextremely difficult, 7

because gel and water have nearly the same density.

One of the objects of the present invention is to make possible a greatreduction in the volume of wash water and the size of washing containersre-' quired. by preventing the product from swelling during washing.This is accomplished by washing with a solution containing volatileelectrolyte which can be completely volatilized from the colloidalsubstance during drying or under the influence of vacuum.

Another object of my invention is to effect a reduction in the timerequired for washing the colloidal substance. This is accomplished byvirtue of the relatively dense structure of the colloidal substance whenmaintained in contact with a high concentration of electrolytes.Relatively little of the wash water is absorbed under these conditions,and the wash water rapidly leaches out the non-volatile impurities fromthe small of colloidal substance is easy, rapid, and positive ascontrasted to the diflicult separation from the Sodium wheat-glutensulphate ordinarily re-' quires a large number of washes to effectsatisf actorily complete remo al of the sodium sulphate remaining in theproduct after neutralization of the excess sulphating acid. During thelater 150 F. and mm. of mercury, absolute).

amass:

3 washes, the washing is inefllcient and time consuming, due to theprogressive swelling of the sodium gluten sulphate as the concentrationof electrolytes is reduced. The final washes are prohibitively timeconsuming from the standpoint of commercial production. on the otherhand, ifa concentration of 5 to of ammonium bicarbonate or othervolatile ammonium salt is maintained in the washing solution at alltimes, the colloidal substance does not swell seriously and theparticles thereof are granular, rapidsettling and free-filtering. Thewashing operation is simple and straightforward and requires no specialprecautions. It can be done either by de-.

cantation or in a filter. When the wash water is substantially free fromsulphate ions, the colloidal substance is dewatered and placed directlyin a vacuum drier. i

In the vacuum drier, the colloidal substance dries readily at moderatetemperatures (at ab lotllit e volatile salt is completely volatilizedduring the drying operation, yielding a salt-free product of maximumgelling power. Tests have shown that prevention of swelling (in' thismanner) during washing does not impair the quality of the final product.Products prepared in this manner have shown, in some cases, a greaterswelling power than other portions of the same batch of material washedand dried by the usual methods.

It is apparent that, in many applications, the concentration of volatileelectrolyte in the washing solution is not critical as long as it ishigh enough to prevent substantial swelling of the colloidal material.It may even be desirable, in some cases, to maintain the wash watersaturated with respect to the volatile electrolyte. In other cases,however, it may be desirable to control the concentration of electrolyteso as to permit a certain amount of swelling in the colloidal material.Further extensions of this idea are obvious.

Some base exchange occurs during washing of the sodium gluten sulfate inammonium bicarbonate solution. The extent of conversion depends upon theconcentration of ammonium bicarbonate and the time consumed in washing.Where base exchange is not desired, washing should be rapid to minimizethe effect. If one desires ammonium gluten sulfate, which has propertieslike those of sodium gluten sulfate, the washing is continued until themetathesis between sodium gluten sulphate and sodium bicarbonate to formammonium gluten sulphate and sodium bicarbonate is complete. Since thesolution of ammonium bicarbonate is present in great excess in thewashing operation it washes away the sodium bicarbonate, decreasing itsconcentration to a negligible level. The rate of metathesis is slow.

Other applications of the invention are apparent to one skilled in theart. In general, many colloidal systems that need to be maintained for atime in a coagulated condition may be so maintained in the presence of amoderate concentration of ammonium bicarbonate, or other volatile salt.When it is desired to repeptize the colloids, the ammonium bicarbonatemay be removed by subjecting the system to a vacuum until theconcentration of ammonium bicarbonate has been reduced to the necessarylow level. v

In still another application of my invention, a finely dividedhydrophilic colloidal substance maybe mixed into a slurry in an ammoniumbicarbonate solution and dispersed throughout a porous body or a cutsurface of the body. The impregnated mass can then be subjected tovacuum to remove the ammonium bicarbonate.

The colloidal substance will then hydrate in situ, yielding a rigidstructure not obtainable by conventional procedures. This method may,for example, be useful in the sectioning of plant or animal tissues. Theabove examples are meant to be typical applications of the invention andnot limiting in their scope. Many other applications of the method of myinvention are readily apparent.

When ammonium bicarbonate is used as the volatile electrolyte in washinghydrophilic colloids, substantially complete recovery of the ammoniumbicarbonate is possible by simply boiling oil. the ammonia and carbondioxide and reabsorbing the evolved gases in water.

Although ammonium bicarbonate is preferred in my process, other volatileelectrolytes obvious to persons skilled in the art may be employed.

'Ammonium carbonate, ammonium carbamate,

ammonium acetate, ammonium sulfite, and ammonium bisulfite may be used,the latter being considered less desirable than the former. Lessvolatile electrolytes require higher temperatures and higher vacuum orboth. Since the colloidal substance is sensitive to heat, the operatormust determine suitable drying temperature and con, ditions and thenemploy an electrolyte of suflicient volatility under such conditions.

The process is capable of wide application to colloidal substances theswelling capacity or swelling rate of which in water increases as theconcentration of electrolytes is decreased and which colloidalsubstances are contaminated by the presence of water-solubleelectrolytes Or other water-soluble impurities. Thus my process isapplicable to such materials as gum karaya, gum tragacanth, alginicacid, salts of alginic acid, low-methoxyl pectinic acids, salts oflow-methoxyl pectinic acids, and other materials of such nature whichare contaminated by the presence of water-soluble electrolytes or otherundesirable water-soluble impurities. Further, my process is applicableto the purification of many proteinous materials such as salts ofsulphated prolamines, salts of sulphated wheat gluten, salts ofsulphated gluten from corn or other sources, salts of sulphated casein,and other salts of sulphated proteins. Thus my process is applicable tothe treatment of any hydrophilic colloidal substance, the swelling rateof which in water increases as the concentration of electrolytes isdecreased and which is contaminated by the presence of watersolubleelectrolytes or other water-soluble impurities. Obviously the questionof whether or not the process is applicable to a particular colloidalsubstance can be readily determined by application of my teaching. Thephysical form in which the colloidal substance is subjected to thewashing is not critical. Generally, it is best to apply the treatment tothe colloidal substance which is in the form of a granular solidmaterial so that maximum rate of separation from the wash liquid will beobtained. However, the treatment can also be applied to colloidalmaterial which is partially solvated to form a gel but which'is stillsumciently rigid so that during the washing, particles of said gel willremain as individual particles and not cohere together as a single, softmass.

While the description of the invention has been confined to aqueoussystems, other solvents may be used in some cases. The scope of theinvention is limited only by the appended claims. 1 Having thusdescribed my invention, I claim:

1. A process comprising washing an organic hydrophilic colloidalsubstance contaminated with water-soluble impurities, the swellingcapacity of which colloidal substance increases as the concentration ofelectrolytes is decreased, with an aqueous solution of a salt of ammoniaand a weak, volatile acid, said salt being vaporizable at a temperaturebelow that at which the colloidal substance is degraded, andsubsequently drying the washed colloidal substance and removing the saltby vaporization.

2. A process comprising washing an organic hydrophillic colloidalsubstance contaminated with water-soluble impurities, the swellingcapacity of which colloidal substance increases as the concentration ofelectrolytes is decreased, with an aqueous solution of a salt of ammoniaand a weak, volatile acid, said salt being vaporizable at a temperaturebelow that at which the colloidal substance is degraded, said solutionhaving a concentration of about-5% to about and subsequently drying thewashed colloidal substance and removing the salt by vaporization.

3. The process of claim 1, in which the colloidal substance is a salt ofa sulphated protein.

4. The process of claim 1, in which the colloidal substance is a salt ofsulphated gluten.

5. The process of claiml, in which the colloidal substance is an alkalimetal salt of sulphated luten.

6. The process of claim 1, in which the colloidal substance is thesodium salt of sulphated gluten.

7. The process of claim 1, in which the colloidal substance is a salt ofa sulphated protein and the said salt is a carbonate of ammonia.

8. The process of claim 1, in which the colloidal substance is thesodium salt of sulphated gluten and the said salt is a carbonate ofammonia.

9. A process comprising washing an organic.

hydrophillic colloidal substance contaminated with water-solubleimpurities, the swelling capacity Of which colloidal substance increasesas the concentration of electrolytes is decreased with an aqueoussolution of a salt of ammonia and a weak volatile acid, said salt beingvaporizable at a temperature below that at which the colloidal substanceis degraded, and subsequently drying the washed colloidal substance andremoving the said vaporizable electrolyte by vaporization at atemperature below that which will reduce the subsequent swelling powerof the colloidal substance.

10. The process of claim 9, in which the colloidal substance is analkali metal salt of sulphated gluten and the said salt is a carbonateof ammonia.

11. The process of claim 9 in which the colloidal substance is thesodium salt of sulphated wheat gluten and the said salt is ammoniumbicarbonate in a concentration from 5 to 10% in the aqueous washingsolution, and in which the drying step is under vacuum, ammoniumbicarbonate being removed from the gel during the vacuum drying.

12 The process of claim 11 in which the washing with ammoniumbicarbonate is continued until substantially all of the sodium glutensulphate is converted into ammonium gluten sulphate.

WILLIAM D. RAMAGE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,457,466 Smith June 5, 19232,341,381 Jelley et al. Feb. 8, 1944 2,423,773 Hart et al. July 8, 1947

